eloso

Hi, I want my arduino and gsm shield to be powered even on power failure. I have one 12V 3A acdc adaptor and 6V 4.5 AH lead acid battery. I'm thinking of using a relay or a diode. which one is better? I already have a 1N5822 schotkky diode for lower voltage drop.

Charging sla's aren't that bad, they are pretty robust(I toture them often with electrically abusive experiments), probably the most effecient way would be a mosfet, a regular diode would only be worth it at low currents, a germanium diode is better but still has current limitations(as well as heat)Basically for that size battery you will want to charge it @.3-1amp constant current untill it reaches close to 13.8, then you have it constant voltage @13.8Easiest way is to use a lm317 although @1amp you will need a heatsink